var keywordsList = ['gtx3090', '机械键盘', '超大电视', '海尔冰箱', '西门子洗衣机'];
var search_input = document.querySelector('.search input');
var keyIndex = 0;
console.log(search_input);
search_input.placeholder = keywordsList[0];
setInterval(function () {
keyIndex = ++keyIndex >= keywordsList.length - 1 ? 0 : keyIndex;
search_input.placeholder = keywordsList[keyIndex];
}, 2000);